The present invention generally relates to a medical administration barrel and a method of sealing the barrel, and, particularly, to a medical administration barrel having grooves assisting in minimizing headspace between a piston and substance within the barrel during the sealing process.
Vacuum piston placement is a piston placement process utilized to insert a piston into an open end of a pre-filled container in order to seal off the substance within the container in an airtight manner from the exterior environment. Generally, the piston and the pre-filled container are exposed to a vacuum, i.e., a pressure lower than atmospheric pressure, and then the piston is thereafter sealingly engaged with the open end of the container. The exterior of the piston and container assembly is thereafter restored to atmospheric pressure, such that a pressure differential is created across the piston between the proximal and distal surfaces thereof. The pressure differential drives the piston down the barrel until the friction force balances the pressure difference. Afterwards, the piston may be further advanced, e.g., by a pushing member, until pressure equilibrium is reached across the piston.
One drawback of the vacuum piston placement process is that where a low volume of substance is filled in a larger container, a large amount of headspace, i.e., the space between the distal surface of the piston and the substance, may still remain after the piston reaches the position associated with pressure equilibrium. For example, the headspace volume may equal approximately 30% of the volume of the substance filled within the container.
One approach to minimizing headspace between the piston and the substance filled inside the container may be to utilize smaller containers. For example, a container may be sized to fit only the piston height, in addition to the length associated with the desired volume of the filled substance. However, where an administration system located behind the piston is utilized to drive the piston forward during use of the container (e.g., when injecting the substance within the container into a recipient), the smaller sized container may not have the necessary space to accommodate the administration system behind the piston. Accordingly, where an administration system is present, the longer container is necessary.
Nonetheless, the sealed container may be exposed to different chemical and/or environmental changes during transport that may potentially cause retraction and ejection of the piston out of the open end of the container. For example, the container may be exposed to sub-atmospheric pressure during air transportation, or travel through high elevation regions, which may lead to retraction of the piston. As another example, the container may be exposed to extreme temperatures, which may lead to retraction of the piston. As yet another example, an internal reaction of the substance within the container may cause a change in headspace gas pressure, which may also lead to retraction of the piston. Further, the relatively large air bubble constituting the headspace and trapped within the container may be problematic when dispensing the substance thereafter.
Therefore, it is desirable to manufacture a container configured to receive the piston and, if employed, an administration system behind the piston, and also assist in further advancing the piston into the container when utilizing the vacuum piston placement process, to minimize headspace volume.